Tephra sequences as indicators of magma evolution: ⁴⁰Ar/³⁹Ar ages and geochemistry of tephra sequences in the southwest Nevada volcanic field

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• 作者：Huysken ; K.T. ; Vogel ; T.A. ; Layer ; P.W.
• 关键词：tephra sequence ; high silica ; magma evolution ; magma mixing ; ⁴⁰Ar/³⁹Ar age ; southwest Nevada
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2001
• 出版时间：April 1, 2001
• 年：2001
• 卷：106
• 期：1-2
• 页码：85-110
• 全文大小：272 K

文摘

Changes in rock chemistry with ⁴⁰Ar/³⁹Ar ages in tephra layers record the temporal and magmatic history of two volcanic systems in southwestern Nevada. Tephra layers from the Post-Grouse Canyon tephra sequence record three distinct groups. These groups are chemically distinct and have ⁴⁰Ar/³⁹Ar ages of 13.52±0.06, 13.31±0.18, and 12.95±0.10Ma. The age groups correspond to three distinct chemical groups based on trace element distributions. These chemical groups cannot be related by any reasonable fractional crystallization or magma mixing model and are interpreted as distinct magma batches. The Pre-Rainier Mesa tephra sequence records two ⁴⁰Ar/³⁹Ar ages (12.79±0.10 and 11.84±0.18Ma). The upper portion of this sequence is equivalent in age and chemistry to part of the overlying Rainier Mesa ash-flow sheet. The lower portion of the sequence is equivalent in age to the underlying Tiva Canyon ash-flow sheet but is chemically distinct from this sheet. The formation of this chemical group is consistent with mixing of low silica Tiva Canyon and high silica, low Th, Rainier Mesa magma.